1. Field of the Invention
This invention relates to a coupler for coupling together plates comprising a male member with male threads and a female member for receiving the male member
2. Prior Art Statement
U S. Pat. No. 4,311,421 discloses a coupler which comprises a male member having a head and a pin-like portion having male threads and depending from the lower surface of the head and a female member having a flange facing the head of the male member, a leg portion depending from the lower end of the flange and a bore extending from the upper surface of the flange into the leg portion and capable of receiving the pin-like portion of the male member. The male and female members are prepared as respective plastic one-piece moldings.
The leg portion of the female member has a pair of axial grooves radially spaced apart around the bore and a pair of spreadable portions formed between the axial grooves and each having an upper end united to the lower end of the flange and a lower end coupled to that of the other via a hinge portion and capable of being spread with the insertion of the pin-like portion into the bore. The inner surface of each of the two spreadable portions is integrally formed with upper and lower semi-spherical projections to be fitted in thread grooves defined between adjacent threads of the male member.
The above prior art coupler, however, has problems in the operation of detaching the male member from the female member by turning the male member in the direction opposite to the direction of the threads.
More specifically, when coupling and fastening together the two plates, the spreadable portions of the female member are spread by forcibly inserting the pin-like portion of the male member into the bore of the female member. To release the coupled state of the two plates, the male member may be turned in the direction opposite to the direction of the threads. As the male member is turned in this direction, the semi-spherical projections in the bore of the female member are moved along the thread grooves in the pin-like portion of the male member. Thus, the pin-like portion of the male member is retreated along the bore of the female member and is detached from the female member.
However, since the semi-spherical projections formed on the surface of the bore of the female member are small, they mesh to a small extent with the thread grooves of the pin-like portion of the male member. For this reason, when the male member is turned for removing it from the female member, the projections will readily clear the threads with application of a force to the male member in a direction of pushing the male member into the bore of the female member.
This leads to idling of the pin-like portion of the male member in the bore of the female member, so that the male member is not readily removed. The idling is liable to occur particularly when the male member is turned quickly by using a motor-driven tool. Therefore, the prior art coupler is not suitable for the male member removal operation using a motor-driven tool.
When the extent of projection of the semi-spherical projections on the surface of the bore of the female member is increased, the extent of mesh of the projections in the thread grooves of the pin-like portion of the male member is increased to eliminate such idling. However, if the extent of projection of the spherical projections is increased, it becomes correspondingly difficult to remove the female member from a mold at the time of molding the female member.
More specifically, FIG. 24 shows a stationary mold 102 for molding the female member 101. The mold 102 comprises a kicker pin 108 for taking out the female member 101 as a product and a core pin 109 for forming the bore 105 of the female member 101. The outer periphery of the core pin 109 is formed with recesses 110 for forming the semi-spherical projections 107 of the female member 101.
When molding the female member 101, the stationary mold 102 and a movable mold (not shown) are butt-closed together, and a molten plastic material is poured into the mold assembly. After the poured material has solidified, the mold assembly is opened by moving the movable mold, and then the female member 101 thus produced is kicked out by the kicker pin 108, while at the same time the core pin 109 is withdrawn from the bore 105 of the female member 101, thus separating the female member from the stationary mold 102. However, when the extent of projection of the semi-spherical projections 107 is increased, it becomes correspondingly difficult to remove the core pin 109, and sometimes the projections that are formed are deformed or broken so that they can no longer fulfill their role. For this reason, the semi-spherical projections have inevitably been small in size. In FIG. 24, reference numerals 103, 104 and 106 respectively designate a flange, a leg portion and axial grooves of the female member 101.